Metal-coated fibers are used in many different products. For example, silver coated, antimicrobial fibers are used in a variety of products in the medical industry because of its bactericidal capability, with proven efficacy against microbes, bacteria, and fungi, and its ability to eliminate odors. Silver coated fibers can be used in wound dressings, clothing for medical personnel, and other fabrics used in the clinical setting. Antimicrobial fibers find use in absorbent materials that contact the skin such as diapers, clothing, bedsheets, bedpads, blankets, and the like. Antimicrobial fibers may be formed with inorganic additives distributed to certain areas of the fiber. Because the antimicrobial agents are only effective when on or near the surface, it is typically desirable that these agents be dispersed throughout a thin coating that is applied to the surface of the fiber.
The antimicrobial characteristics of certain metal-coated fibers are also useful in water and air filtration applications, such as water purifiers and germ-removing filter having fibers bonded with silver ions for sterilizing air. These filters can also be used to filter air that has a substantial amount of recirculated air from confined spaces such as in vehicles and aircraft cabins. The filters are also useful in environments where a high degree of sterility is required such as in hospitals, clean rooms, and food processing and preparation areas. However, before such filters can achieve widespread adoption in many consumer applications, they must be economically priced.
Metal coatings can impart electrical conductivity to nonconductive fibers. The conductivity can be selectively controlled for a given application by varying the type and extent of metal coating applied to the fiber. Metal-coated fibers having a high degree of electrical conductivity have found uses in, for example, the medical industry for certain specific medical devices, fabrics that shield other materials from a dissipated static charge, conductive tapes, and filters as further disclosed herein.
Metal-coated fibers can be used in textiles for imparting antistatic performance. Static electricity can cause a spark discharge of a static electrical charge that has built up, typically as a result of friction, on the surface of a non-conductive material. Consumers prefer fabrics substantially free of static charges that can otherwise interfere with the comfort and enjoyment of the product. The antistatic quality of the fabric can also be important for clothing worn in certain applications such as for preventing static discharge when working with microelectronic equipment and when working in other clean room and clinical settings. The ability to resist static buildup can also make these fibers useful in flexible-shielded enclosures and other packaging materials particularly for storing and shipping sensitive electronics. Preferably, the fibers of these materials are designed to have a requisite type and amount of metal coating needed to impart a sufficient degree of electrical conductivity or low electrical resistivity that allows an electrical charge to dissipate without sparking. This design choice is guided by the proper balance between the cost and the effectiveness of the fabric.
Fibers with metal coatings are also useful for electromagnetic and radio frequency shielding. Electromagnetic and radio frequency shielding can be useful in the medical profession or other industries to prevent such waveforms from interfering with the operation of critical equipment sensitive to such waveforms. Furthermore, metal coated fibers are useful in certain military applications for preventing detection by infrared or radar systems. Certain applications, however, require that a controlled amount of metal coating be applied to the fiber. Also, waste results when more metal than an application requires is deposited on the surface of the fiber. Such waste can significantly increase the expense associated with manufacturing the product, particularly when the metal is a precious and/or expensive metal. This also serves to make the product less economically attractive and less available to the consuming public. One effort to resolve this problem has been to mechanically split a melt spun non-conductive nylon fiber into at least two filaments. One of the filaments is treated with a metal coating. The filaments are then recombined to obtain a yarn having a certain degree of electrical resistance and the needed support structure. However, it is difficult to precisely control the extent of material split into each filament and, as further disclosed herein, it can also be difficult to obtain a consistent distribution of metal on a fiber coated on a continuous processing line depending on the method used to coat the fiber. Therefore, it can be difficult to meet a desired specification for a finished product using the fiber formed by this technique.
Another approach to controlling the extent of activity of the coating applied to the fiber is to vary, for example, the concentration of the active component. However, such coatings can be difficult to formulate and any non-uniform distribution of coating across the surface of the fiber will inevitably cause the rate of antimicrobial activity to vary. U.S. Pat. No. 6,841,244 describes the difficulties involved in evenly dispersing throughout the fiber coatings that contain metals. As noted therein, the problem is exasperated because many of the metal-containing compounds in these coatings are quite large.
Conductive materials have previously been made by blending conductive fibers with other fibers in order to impart electrostatic dissipating capability to the finished fabric. The conductive fibers need to be blended with other fibers in order to control the color and texture of the finished fabric. The coated fibers tend to have a dark color that can lead to color variations, a stiffness that can impart undesirable tactile properties to the fabric, and an abrasive feel due to the conductive particles at the surface of the fiber. Thus, the properties of the blended fiber can be inconsistent across the material because of the problems cited above. Further, blending fibers to achieve the desired conductive properties increases the cost of the finished conductive material. There remains a need in the art for fibers that have a metal disposed only partially across the surface in order to overcome inconsistencies in color, tactile, and other physical properties that can occur in conventional blended fibers and to reduce the cost of materials made therefrom.
Masking processes may be used for selectively distributing a metal on the surface of a non-conducting fiber, and these types of processes generally involve applying a seed material containing a catalytic agent, which facilitates the subsequent electroless metal deposition on the surface of the fiber. This approach requires that the surface of the fiber be thoroughly cleaned before the seed material is applied. In order to achieve a consistent distribution of metal across the surface of the fiber, the seed material itself must be evenly distributed. Inasmuch, the conditions under which the process is carried out and the consistency and composition of the seed material must be tightly controlled in order to achieve a consistent distribution of metal across the surface of the fiber. Further, in order to achieve the desired conductive properties, the seed material must be consistently distributed across the full axial extent of the fiber, while limiting it to only a certain circumferential area, a process that can be difficult to achieve using conventional masking operations.
One attempt at making a fiber that is partially nonconductive and partially conductive includes disposing graphite or metal particles throughout a polymer, however, the conductive material is not disposed substantially at the surface of the component. Furthermore, the fiber does not address the cost barrier associated with disposing materials substantially circumferentially about the surface of the fiber particularly when an application requires the use of higher priced metals.
There remains in the art a need for a fiber whose surface can be selectively coated with a metal. Further, the art requires a fiber that is partially coated whereby the coating becomes substantially adhered to a receptive surface. Additionally, there remains in the art a need for a fiber whose surface can be selectively coated with a metal and yet provide the metal-coated fiber with other advantageous properties such as flame retardance and chemical resistance.